[Elecraft] Microham Microkeyer II, RFI in mike with my K3

Tue Feb 16 02:04:35 EST 2016

Bernhard,

It's NOT common mode, it's the simple fact that the audio interface is a 
mess. The antenna on the roof transmitting high power is doing its job, 
putting a lot of RF in the shack. If it didn't (based on proxmiity), it 
would be a lousy antenna. The problem is that the interface (wiring plus 
electronics plus termination) does not reject RF because it fails to 
conform to fundamental principles that reject RF. That is, every cable 
must be a transmission line, every shield must be terminated at the 
shielding enclosure of the equipment at both ends, and every equipment 
chassis must have a short, fat, bond to every other equipment chassis. 
Yes, the signal is audio, but the interference is RF, and it takes 
proper transmission line techniques to reject that RF.

I have VERY limited experience with MicroHam, but the jumble of wires 
that I encountered with the MicroHam unit at W6OAT violated all 
principles of good engineering practice for operation in a high RF 
environment. It was nothing more than a multipin connector with a lot of 
wires soldered to that connector.  Indeed, it would darn near impossible 
to do it right without starting from scratch withunit a properly made 
cable from the MicroHam unit to the radio, with each signal path having 
its own coaxial cable.

I have no idea if that describes ALL MicroHam units, but it does 
describe Rusty's. And don't ask the model number -- I was so disgusted 
by what I saw that I just rolled my eyes.

73, Jim K9YC

On Mon,2/15/2016 10:43 PM, Bernhard.Horst at bmw.de wrote:
> Hi Guy,
>
> Fully agree with your statement, but as stated I have chokes in all Coax, rotor and control cables.
> I am using double shielded USB cables, extra grounding for each device…no idea what else could be don.
> Regarding the 2 Ohm, there is a recommendation by Microham to check that the USB / Molex connector resistance should not exceed 5 Ohm otherwise your PC has a USB/Chassis grounding problem.
>
> I had RFI in the Microham already with 300Wtts…now I can run 1200Watts without any problems with is over the legal limit over here anyway!
>
> Several HAMs observed problems with the Microham and in combination with K3/other rigs.
> The cheap homebrew USB/Soundcard interface works now, that’s all what counts.
>
> 73
> Bernie
> DL5RDP
>
> Von: guyk2av at gmail.com [mailto:guyk2av at gmail.com] Im Auftrag von Guy Olinger K2AV
> Gesendet: Montag, 15. Februar 2016 18:15
> An: Horst Bernhard, MZ-LR; Elecraft Reflector
> Betreff: [Elecraft] Microham Microkeyer II, RFI in mike with my K3
>
> Hi Bernie,
>
> If you are running QRO over your roof, your RFI proofing needs to be perfect. Your situation is only exceeded in nastiness by being next door to a 50 kW AM station and maybe not then. Your induced common mode RF voltages on conductors can be double and triple the desired signal voltages on the cables and ridiculously more than microphone voltages.
>
> One CAN get lucky and get by, but if one does it's only by dumb blind luck and any change to cable routing or position and count of station equipment can disable or polute electronic functions.
>
> If you succumb to the temptation to attribute the changes to the last thing changed or moved, you will be sent down the rabbit hole to join company with Alice and the Mad Hatter where nothing makes sense any more. This can include complaints to manufacturers straight from Wonderland requiring apologies afterward. Been there, done that. Know whereof I speak.
>
> It is quite probable that replacing the box changed cable specifics. Any connection that is not a tenth of an ohm or less needs to be replaced or repaired. I have no idea where you got 2 ohms as a satisfactory connection resistance. Maybe the USB signal itself will tolerate that under otherwise non-stressed circumstances but it's far away out of bounds for RFI proofing.
>
> In your case, QRO on the roof, you need to take maximum anti-RF measures on **ALL** conductors in the shack. Otherwise just changing orientation of cables may remove or incite RFI, or worse makes RFI intermittent leading to suspicions of poltergeist.
>
> I have finally gotten to the point where all retail audio cables need to be replaced with soldered coax or shielded pairs with WOVEN shields. ESPECIALLY audio cables terminated in RCA plugs which typically have the cheapest shields known to man. No retail manufacturer is testing them for RFI susceptibility in rooftop QRO conditions.
>
> There is a good selection of shielded pair and coax cable with Teflon dielectric/insulation and woven shields easily soldered to *quality* RCA plugs or other connectors without melting the wire.
>
> I know that QRO on the roof is all that's available for many folks. Just understand that's the very stiffest possible demand on all RFI proofing issues. No cheapies, no short cuts, no omissions allowed in the protocol.
>
> 73, Guy K2AV
>
> On Monday, February 15, 2016, <Bernhard.Horst at bmw.de<javascript:_e(%7B%7D,'cvml','Bernhard.Horst at bmw.de');>> wrote:
> Dear all,
>
> just an update..the Microham Microkeyer II has definitely a problem with RF!
> I replaced the Microkeyer with a homebrew USB and soundcard interface (Built in 2008) and made new cable distribution box..And the problems are gone.
>
> I have S-NO 280 on the microkeyer..hope the newer ones are better. But definitely not my kind of solution for that cost!
>
> 73s
> Bernie
> DL5RDP
>
> -----Ursprüngliche Nachricht-----
> Von: Joe Subich, W4TV [mailto:lists at subich.com]
> Gesendet: Freitag, 12. Februar 2016 14:15
> An: elecraft at mailman.qth.net<mailto:elecraft at mailman.qth.net>
> Betreff: Re: [Elecraft] Microham Microkeyer II, RFI in mike with my K3
>
>
>> As I recall, I used pin 7 for the mic ground and pin 8 for the PTT
>> ground. In a brief test it worked ok into a dummy load. Is this not
>> correct?
> That is correct although with the K3/K3S since the Elecraft mic RFI
> change it should not matter (both pin 7 and pin 8 are connected to
> the "ground" foil on the front panel circuit board).
>
> Early K3 front panels included an RF choke in the mic *and* PTT returns
> which made the "pin 1 problem" much worse.  With the RF choke removed
> (bypassed) the issue is significantly reduced but there may still be a
> problem if the overall station installation has any "RF on the coax."
>
> 73,
>
>     ... Joe, W4TV
>
>
> On 2/12/2016 7:59 AM, john at kk9a.com<mailto:john at kk9a.com> wrote:
>> This week I wired rewired my MicroHAM Micro2R cables for K3S's.  As I
>> recall, I used pin 7 for the mic ground and pin 8 for the PTT ground. In a
>> brief test it worked ok into a dummy load. Is this not correct?
>>
>> John KK9A
>>
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